Electrolytic method and apparatus for the manufacture of tapered conductors



July 29, 1952 T. B. GIBBS T AL ELECTROLYTIC METHOD AND APPARATUS FOR THEMANUFACTURE OF TAPERED CONDUCTORS 5 Sheets-Sheet 1 Filed ll arbh 9, i944& Y R 5 w M m Msn 0 VMTM. T T 1.6M H w 3 0mm Z? July 29, 1952 Filedlarch 9, .1944

T. B. GIBBS ETAL I ELECTROLYTIC wg'mon AND APPARATUS FOR THE.IIANUFACTURE 0F TAPERED CONDUCTORS 5 Sheets-Sheet 2 l7 I8 63 I22 24 I?20 INVENTOR.

filo/-14: 5. Glass SHHUEL Dm/sas'rr/u HTTOE/VE Y y 9, 1952 'r. B. GIBBSEIAL 2,605,218

' ELECTROLYTIC METHOD AND APPARATUS FOR THE MANUFAGTURE 0F TAPEREDCONDUGTORS Filed March 9, 1944 5 Sheets-Sheet 3 IZ/ v /22 y 1 1 I 1 I 1H /3 i i g /4 lo /00 9a ATTORNEY July 29, 1952 Filed March 9, 1944 T. B.GIBBS ETAL ELECTROLYTIC METHOD AND APPARATUS FOR THE 5 Sheets-Sheet 5MANUFACTURE OF TAPERED CONDUCTORS Emma 5 6755s Sq/vun D/A/fESTE/N 6:02 5k/GVLMAN Patented July 29, 1952 ELECTROLYTIC METHOD AND APPARATUS FORTHE MANUFACTURE "OF TA PERED CONDUCTORS Thomas B. Gibbs, DelavanLakeQSam'uel Dinerstein, Delavan, and GeorgeW. Gilman, Janesville, Wis.,assignors to The George Borg Corporation, Chicago, Ill., a corporationof Delaware Application March9, 1944., serial No, 525,764

The present invention relatesto methods and apparatus for themanufacture of tapered conj ductors, and the object of the invention isto I produce new and improved methods and apparatus of this character,whereby tapered conductors in a variety of forms may be produced in areasonable time and at small cost.

Tapered conductors such as referred to herein may be used for variouspurposes, but an important use is in the manufacture of non-linearrheostats or potentiometers. By a non-linear Y potentiometer is meant apotentiometer in which equal movements of the slider from differentstarting positions result in unequal changes'in" resistance. Suchpotentiometers have been constructed by winding resistance wire on atapered form, and potentiometers constructed in this way aresatisfactory for some purposes. objections, however, such asdifficulties in windingand the impossibility of obtaining a rapidincrease in the resistance per turn without unduly increasing the sizeof the potentiometer. 1

Non-linear potentiometers have also been constructed by means of atapered conductor-which is made by; splicing together short sections ofresistance wire of different diameters."

which tap'ers by stages, or step-wise, from oneend to the other. For apractical potentiometer, however, the number of steps must be ratherlarge andthe cost of splicing the numerous sections 3 Claims. (Cl.204-442)..

There are l Utiliz'-' ing this'method, a tapered conductor is producedrequired is high. There are also winding diffi-' culties.

cessful;

The foregoing will make evident the need for" Hensce, this method is"not very sucadapting it for use in the construction of nonlinearpotentiometers. by the present invention, which makes it pos-' Thisrequirement is met sible to manufacture such conductorsfor the firsttime, so far as known.

According to the invention, a tapered conductor is manufactured from aconductor of uniform cross-section by subjecting the wire to anodicreduction 'in an electrolytic bath; The Wire is drawnthrough the bath ata relatively high speed at first; and the taper is produced bygradually" decreasing the speed, thereby progressively increasing thetime in the bath and the amount of metal removed from the wire. Theresulting wire has the original diameter at one end and anyimposedhereby the minimum tensilestrength requirements. In practice wire hasbeen reduced from a diameter on the order of 4 or 5 mils. on larger to adiameter of .9 mil, which about the smallest size of wire that has theneoessary mechanical strength.

It maybe pointed out, moreover, that by suitably varying the rate atwhich the speed .is

changed, different forms of taper can be produced. A

Thus, tapers corresponding to' various exponential curves can be,produced as well as a straight line or conical taper. I

While the principle employed is relatively simple, the application ofthe principle to the successful manufacture of tapered wires in commercial' quantities is attended with many difficulties. To mention justa few of these difiiculties, the amount .of metal removed from a wireundergoing treatment'is not only dependent upon the time in the bath,but upon the value of the current and upon the anode current efiiciency.The current tends to vary in accordance with the size of the Wireexposed to the action of. the bath, which becomes progressivelysmalleras the process continues. The anode cur- .rent efficiency' varieswith the temperature of resistance wire, having low conductivity,result-.

ing in the fact that the current required for commercial operation ofthe process is many times greater than the carrying capacity of the.wire. A still further problem is introduced by the fact that althoughthe resistance wire material has a fair tensile strength, many of thetapered wires which have to be made are extremely fine and are ratherweak at the small end, therefore. The

strength of some of thesefine Wires is measured "in ouncesrather. thanin pounds. This makes it impossible ,to use any type of pulley system toguide:v the wire repeatedly through the electrolytic bath. The forcerequired to pull the wire through a'system of this kind would break thewire before the required reduction in diameter is'obtained. The makingof a good electrical connection to the moving Wire is another problem,especially since any friction produced would increase the force requiredto move the Wire.

The foregoing and other problems are solved so that no part of any wirehas to' carry morethan a small fraction of the total current.Compartments containing mercury are arranged alternately with theelectrolytic'cells for this'pur'-' pose. The substantially frictionlessnature of the sliding connections formed by the'm'ercury} coupled withthe fact that the wires move through the mercury compartments and theelectrolytic cells on straight lines, makes the force required to movethe wires very small. a

It may also be mentioned at this time that the successful operation ofthe invention from the standpoint of producing tapered conductors withpredetermined tapers, reproducible at will, is due in large part totheelimination of all-variable factors which aifect the rate .of anodicreduction, with the single exception of] the time factor. The time inthe bath, depending onthe rate at whichthe wire is pulled throughthebath, is rigidly controlled in accordance with the'particular'form oftaper to be produced.

Proceeding now withthe detailed explanation, the apparatus will first bedescribed, reference being'had to the accompanying drawings, in which-Fig. 1 is a more or less diagrammatic view showing in elevation some ofthe principal parts of the electrolyte circulating system, including themain and auxiliaryv tanks; r r

Fig. 2 shows the electrolytic cell system in elevation, and also thearrangement for supporting the spools containing Wire .to be processed;

Fig. 3 is a plan view of the electrolytic cell system; 1

4 lytic cells from left to right by means of the transfer or take-upspools such as IE8, Fig. 5.

It will be convenient to describe the electrolytic cell systemfirst,reference being had to Figs. 2, 3 and 4, and also to the detail drawingsFigs. to 13, inclusive.

The reference character It indicates the top of a bench, table or othersupport, referred to- Fig. i is a cross-section on the line Fig. 2

pulling mechanism in Fig. 10 is a section onthe line |Bl0, Fig. 9;

Fig. 11 is a section on the line lI-ll, Fig.9;-

Fig. 12 is 'a'section on the linef l2'l'2, Fig. 9;

Fig. 13 is a supplementary drawing showing-the arrangement for guidingtheprocessed wires onto the take-up spools; and

Fig. 14 is a'diag'rammatic'layout of a tapered wire."

Figs; 1, 2 and 5, when properly arranged, show the complete apparatus inelevation. In order to connect these drawings, the sheets bearing Figs.1 and 5 should be placed upright, with the sheet bearing Fig. 2 betweenthemand on its side and the sheets should be adjusted so that the brokenparts of the bench, table, or base ID are in-alignment. ,When the sheetsare thus arranged the drawings show the electrolytic cell system, Fig.2, inthe center, with the electrolyte supplyon the left, Fig. l, and thewire pullingmecham'sm on the right, Fig. 5. The wires or conductorsbeing processed are carried on the spools such hereinafter as a base,which is conveniently lo-' jcated about 3 ,or 4 feet above the floor sothat the parts mounted on the base will be readily accessible totheoperator. The base may be of wood {for any suitable material.

The electrolytic cells are supported upon two parallel spaced strips Hand I2, which are held in position a short distance above the base ID bymeans of :a number of brackets such as [3 and M, Fig. 4, and I4 and 15,Fig. 2. These strips may alsobe of wood, and together with the base ID,are preferably given a coating of acidproof paint. The cells arearranged on the tWo strips l I and l 2..iii-a row extending parallel tothe strips as shownin Figs. ,2 and 3, and each cell rests partly onstrip H and partly on strip I2, bridging the spacebetween them, as seenclearly in Fig. 4.

The number of electrolytic cells is variable, but there should be aconsiderable number of them. There may be, for example, It completeelectrolytic cells, of which only a few are shown in Figs. 2 and 3. Eachcell is made in two sections, which may be referred to as cathode andelectrical contact sections, respectively. The cathode and electricalcontact-sections alternate in the cell assembly. Thus, thesections 16,I8, 20, etc. are electrical contact sections, while the sections I1,

I 9, etc. are cathode sections. The sections l 6 andl'! may be regardedas constituting the first electrolytic cell, sections [8 and i9, thesecond, and

so on.

Due to the arrangementof the cells in a compact row, however, thecathode section of each cell has adjacent thereto on the right theelectrical contact section of the next'cell, that is,

each cathode-section is between'two electrical contact sections, thelast electrical contact section 23 being added to carry out thearrangement. From a functional standpoint, therefore,"

each compete electrolyte cell may be regarded as being composed of acathode section and two. electrical contact sections. Considered on,this basis, the'sections l6, I1 and it constitute the, first cell,sections lfl, I9 and 2D, the second, and:

sections 2 l, 22 and 23, the last, each electrical contact sectionexcept the end sections l6 and 23 being common to two cells.

Before going any farther into the cell assembly it will be well toexplain the structure of the in-.

dividual cell sections, reference being had to Figs. 10 to 13,inclusive, which, show the electrical contact section l8 and the cathodesection IS; The electrical contact sections are all like section 18 andthe cathode sections are a1 like section I9, so it will be sufficient todescribe these two sections.

The sections may be made of variou materials. and may be constructed invarious ways. proof material should be used; or the cells should becoated with acidproof paint. A convenient material to use ispolystyrene, which is notattackedby the acids of which the electrolyteis composed. The sections shown are made from solid blocks ofpolystyrene by machining an drilling operations.

Theeleotrical contact section It) has a plurality.

Acidthe' compartments which contain Water or elec-' trolyte'are notleakproof. Certain of .the compartments are provided to take. care ofthe leakageproblem which thus arises. This will all 'be fullyexplained."

Considering the cathode section 19, there is a single rectangularcompartment 24, for electrolyte, having. the slotted end walls 25 and26. There are four slots such :as 21 and 28 in each end wall. The widthof the slots should be just slightly greater than the diameter ofthelargest wire to be processed and may be .012 inchyfor example, or 12mils. The depth of the slots is about one-half the height of the Wallsas will be clear from the showing of slot 21, Fig. 11.

Electrolyte is supplied to the compartment 24 through a nipple 30, whichis set into an opening 32, Fig. 12, communicating with the bore 3|extending lengthwise through the cathode section 19,. as indicated bythe dotted lines in Fig.10.

The bore 3| is intersected by the cross bore 33, Figs. and 12, the endof which is closed by the plug 34'. This cross bore supplies electrolyteto the four nozzles 35, 36, 3'! and 38, which are set in openingsdrilled in the bottom of the compartment 24 to meet the cross bore 33.The construction of the nozzles will be clear from Figs. 10 and 12. Eachnozzle has a single rather small opening such as 31 arranged to directthe fiow'of electrolyte upward and toward the opposite end of the cell.It will be noted that the four nozzles are in alignment, respectively,with the four conductor slots such as 2'! in the wall 25 of thecompartment 24. There are two overflow tubes, indicated at 3 and 40',Figs. 9 and 11. These-tubes are set in holes drilled in the bottom ofthe compartment 24 to meet the cross bore M, the end of which is closedby the plug 42. serted in another hole which is drilled up through thebottom to intersect the cross bore 4|.

The nipple 39, nozzles 35-38,; plugs 34 and 42, I

The drain pipe 43 is in-,-

and tubes 39, 49 and 43 are preferably made of polystyrene.

solving polystyrene in a suitable organic solvent.

The solvent evaporates after the. parts are assembled and leaves themfirmly attached to the main block of which the cathode section isfabricated.

The longitudinal bore 3| in the cathode sec- 7 tion i9 is in alignmentwith similar bores in all both ends by polystyrene plugs, or the boresmay.

Before assembly the contacting surfaces are painted with a cement madeby disbe omitted from theend sections l6 and 23. Electrolyte is suppliedto the conduit bymeans of a number of tubes whichvconnectwith nipplessuch as 39 as will shortly beexplain'ed. The direction of flow throughthe cathodej'section' l9,

may be traced at this time, howeverq The clec-i. trolyte passes from theconduit(bore 3|) to the cross bore 33, and from the cross bore it issupplied to the compartment 24 by the four nozzles 3548. The compartment24 is maintained full of electrolyte up to the top of the overflow tubes39 and 49, the surplus passing down these tubes to the cross bore 4|from which it is drained off i through the drain pipe 43. The collectionof the electrolyte *fromithe drain pipes suchas 43, and

its return to the circulating system will be explained later. ,1

The cathode is indicated by the reference char-- acter 44, Fig, 9, andcomprises-a horizontal section 45, which rests on the bottom of thecom-- partment24, a vertical section 45 whichex'tends upward out of thecompartment, and a short horizontal section 4! which extendspartly overthe rear wall of the compartment. The-cathode is shown in Figs. 9, 10and 11 but the shape there-' of is best seen in Fig, 11. The cathode isprefer-.-v ably made of a special graphite which is sold 1 under thetrade-mark Karbatefr This material is very dense, having a porosity ofless than 1%,

and has relatively high heat-and electrical con'- ductivity as comparedto other forms of carbon.

The section 41 ofthe cathode should be copper plated so that a conductorcan be soldered onyas indicated in Fig. 3. Then the sections 41 and'46are coated with acid'prooi paint so that only the section 45 will beeffectively in contact with electrolyte.

Consideringthe electrical'contact section l8 now, the first compartment'48 at theleft is an electrolyte collecting compartmentand is providedto collect the electrolyte that leaks through A low partition 5iseparates compartment 48 from the second compartment 52, which is awater collectingcompartment, provided to collect the Water which leaksthrough the slotted partition 55.

drains off the water as fast as it is collected. To the right of thepartition 551s the Washing compartment 56, which is provided with anoverflow tube 51, set in a hole drilled through the bottom of thecompartment. At the opposite end of the hole the drain pipe 6| isinserted.

The next compartment is the mercury'compartment, formed, by thepartitions 59 and 62.

This compartment is rece-ssedat the bottom to receive a rod 63, madepreferably of some metal such as molybdenum which is a fairly goodconductor and is not readily attacked by mercury. The terminal screw 63passes through a 'hole drilled in the front wall of the compartment 59of rod 60. The rod 69 is drawn up against the rod 60.

to be connected to the terminal screw 63.

The compartment 59 is filled withrnercury up -to a short distance belowthe top of partition 58, or well above the bOaomS; -or the slots in'the' various partitions and walls which receive the" conductors beingprocessed. pass through the mercury; therefore, which is provided inorder to make a good sliding connection to the moving conductors fromthe terminal 53. Therod G3 is provided in order to make the" resistancebetween the terminal and the several conductors substantially the same.

The mercury does not leak out of compartment 59 through the slots in'the'partitions 58 and 62,

due to the narrow width of the slots andto the fact that the mercurydoes not Wet the polysty- 4 rene of which the partitions are composednor A hole 53 in the bottom of com-' partment 52' connects with thedrain pipe 54'and I The rod '69 is drawn up against the wall of thecompartment by means of a' nut. 64, a Washer 655 being interposed toseal the opening if desired, although this is not strictly necessary. Asecond nut'65 is provided to enable a conductor These conductors'section I9.

the conductors being "processed. The "surface tension .of the mercury,therefore, prevents its escape through the slots in the partitions.

Water is continuously supplied :to the mercury compartment 59 :by anarrangement which will be described shortly.- tThe water overflows thepartition .53 and fills the washing compartment 5.6 :up to the :top ofthe overflow'tube 51, through whichtit-drains-ofi.

:To the right of the mercury compartment 59 there "are two compartments61 and '69 whichare separatedby the 'lowpartition &8. Compartment SIisprovided to collect the water which leaks through the slot-ted partition=62 while compartment 'lIiB'Jis-fOr collecting the electrotype thatleaks through the slotted wall 26 of the electrolyte compartment 24- ofthe adjacent cathode The compartments 161 and 69-have holes :drilled inthe bottom in which there are inserted the drainage-pipes I and ll.

Fihewarious tubes or pipes of the-anode section I8, such as 50, 54, etc.are attached by means .of polystyrene cement, as in the case of thecathode section 1:9. It will be understood of course that the sectionsthemselves are secured together in the same way. When assembled andcemented together the sections become firmly united and thestructure isas rigid andstrong as if fabricated .f-romzone continuous block ofpolystyrene.

The main electrolyte tank .is indicated at I3, Fig. 1, and is supportedon a suitable sub-base I6 by means of brackets such as 74 and 1 5, thearrangement being such .that the tank 13 is below the .level of the base.10. The tank I3 may be made of any suitable material. of sheet steel,.for example, and in this case is coated with acidproof paint.

Suitable .means is provided for heating the tank I3, shown as comprisinga Bunsen burner I7. The .supply of gas to the burner is controlledbymeans of a manua ly operated valve I9 and an electromagneticallyoperated valve 80. The reference numeral 1-8 indicates a heavy metalplate secured to the bottom .of the tank to distribute the .heat fromthe burner.

addition to the main electrolyte tank 13 there .is an auxiliary tank 8|,which is supported about .3 .feet above the base I0 in any suitablemanner, as by means of an upright member 82.

The electrolyte is transferred from the main tank I3 to .the auxiliarytank ill by means of a centrifugal pump v83, driven by the motor 04. Thepump .83 may be of known construction, adapted .for pumping acid. Thecasing and impellor may be made of polystyrene, for example,

and theshaft of .stainlesssteel.

.The electrolyte flows from the pump 83 to the tank B-I through .a hoseconnection 85. Rubber hose maybe used here, as it is for otherconnections to .be described. The tank-8| .is maintained full=ofelectrolyte to the top .of the overflow pipe 86, and supplieselectrolyte to the electrolytic cells, as will be described. The excessoverflows through the pipe 86 and passes by way of the hose-connections.81 and 0.9 to the vessel 90,0011- taininga hydrometer 90'. A constantlevel in the vessel 90 is maintained by the overflow connection v91.,through which the excess electrolyte returns .to themaintank .13. The Yconnection 08 and the short hose.92, open at the upper end, are

provided .in order to get rid of air entrapped in the overflow from thetank BI .and thus avoid an excess of bubbles in the vessel 90, whichwould otherwise interfere with .the reading of the hydrometer.

It may be made electrolytic cell system at a plurality of points,

tending to equalize the pressure at all .the cells.

The wash water is supplied to theelectrolytic cell system through a pipeI03, which is connected to the water supplysystem througha hoseconnection I04 and a valve I05. The .pipe I03 :is supported on .thestrip II by means of brackets such .as .106, as shown .in Fig. 4, and isequipped witha plurality of nozzles such as I01, I08, etc., one for eachelectrical contact section, 'by:means of which water is delivered to themercury compartments of such sections. The Water pressure may beregulated by the valve I05 and shouldibe sufiicient to maintain a goodcirculation through the washing compartments such as 50.

The arrangement for collecting the electrolyte and wash waterfrom theelectrolytic .cellsystem may now be described. Referring to Figs. 2 and4, .it will beseen that two troughs 96 and :9] are provided, which aresupported on the base I0 by means of blocks suchxas I00 and which extendbeneath and parallel .to the electrolytic cell system. The troughs areso disposed that all the drain .pipes such ,as 50, '50, :II, 4.3, etC.which carry electrolyte, empty into the trough 96, whereas the drainpipes such as '54, .54, i6.I, 10, etc., which carry water, empty intothe trough 9.1. The trough 96 has an outlet pipe 98 and a hoseconnection I501, by means .of which the electrolyte collecting in thetrough is drained back to the main tank I3. The trough 9'! has an outletpipe 99 and a hose connection I02, by means .of which "the :watercollecting in the trough is disposed of.

Returning now to Fig. 1, it wasmentioned that the main tank I3 is heatedby suitable means such as the Bunsen burner 11. The flow .of gas to theburner is adjusted by means of the valve I9 so that the .burner isadapted to maintain'the electrolyte at a temperature which is somewhathigher than the desired or optimum temperature and means is provided tocool the electrolyte whenever its temperature rises slightly above thedesired value. The cooling means comprises one or more coils of glasstubing IIO. Water is supplied to the tubing IIO through a hand valve 3',an electromagnetically operated valve H2, and a hose connection I I I.The hose connection II4 leads to the waste pipe or drain.

The valve 3' is open when the apparatus is in operation and theadmission of water to the cooling coil H0 is controlled by the valveIIZ, which in turn is controlled by the relay I I3. The relay circuitincludes conductors H4 and .I I5 which lead to a thermally operatedswitch I16 which is immersed in the electrolyte in the main tank. Whenthe temperature .of the electrolyte rises to a predetermined point whichis slightly higher than the desired temperature the switch II 6 closesthe circuit of relay 3 and the .relay energizes. The operation of therelay closes a circuit for the electromagnetically operated valve itshortly begins to fall with the result that the switch IIS opens, therelay H3 is deenergized, and the valve H2 is closed again. 7

Fig. 1 also shows the power leads I I1 and H8, which maybe connected toany convenient A. C.

outlet. From these leads current is supplied to the motor 84, relay H3and the electromagnetically operated valves 80 and H2. A switch H9controls the circuit of the motor 84 and the circuit of valve 80.Another switch I is in the circuits of relay H3 and valve I I2.

The electrical connections to the 'electrolytic cells may now beexplained. Twobus bars are provided, which may be made of copper tubing,and are attachedin suitable manner to the outside edges of the strips IIand I2. They extend throughout the length of the electrolytic cellassembly. All the cathodes are connected in parallel to the bus bar I2Iby means of short conductors such as I23, which are soldered to thecathodes and to the bus bar. All the terminals such as 63 are connectedin a similar mane ner to the bus bar I22. 1 5.

Power for the electrolytic cells may be supplied by a motor generatorset, of which only the generator I is shown. As indicated, the generatorI25 is a shunt wound, direct current generator,

with field rheostat. -The negative and positive output leads from thegenerator terminate, in. a double pole double; throw switch I34, whichin one position connects the generator to an artificial load comprisingthe resistance l32 and rheostat I33, and in the other position connectsthe generator to the conductors I35 and'ISE, which are connected to thebus bars I2I and I22 respectively. Associated with the'positive side ofthe circuit there are a plurality of current regulating devices each of,which is provided with an individual switch such as I21. Six of thesede vic'es are preferably of two ampere capacity, while the seventh is ofone ampere capacity. I An ammeter E28 is connected in the negative sideof the circuit. A high'shunt resistance I29} in series with the rheostatI30, provides for a. fine adjust-' ment of the output.

The conductors or wires to be processed are wound onspools fromwhich'they are drawn ofi during the processing operation. Fig. 2 showsfour spools I40, I4I, I42 and I43 carrying four wires I50, I5I, I52 andI53, respectively, which have been connected up preparatory to pullingthem through the electrolytic cell system.

The spools I -I43 are carried on a diagonally disposed cross member Iwhich is secured to a vertical support I44 mounted on the base 10. Thespools are rotatable to permit the wires to be drawn off, but, rotationof the spools is opposed by individual friction brakes inorder to keepthe wires taut. There is a U shaped'b'racket I45 which is suitablyattached to the cross member I45. The spool-I43 iscarriedon'a shaft I41which is rotatable in bearings formedflby semi-circular notches cut inthe ends of the two legs of bracket I46. The shaft I41 has anenlargedcentral por tion which atone end is a little larger' than 'thehole in the spool, being made with a slight taper, however, so that thespool can readily be pressed onto the shaft byhandor removed therefrom.-The pulley I48 is. fixed to the shaft I4,1iand.sup-

ports a weight I49, by means of a-izcord I54. v When the spool isrotated by drawing off the wire I53, the shaft I41 and pulley I48'rotatewith -it,"the, rotation being opposed by the weighted; cord which slipsin the pulley'groove. Weights of different sizes may be provided, andtheyare preferably slotted like scale weights so that they fAfterleaving the spools Mil-I43, the wires- I5 0-.I53.pass beneath thegrooved rod I55 before entering the electrolytic cell system. Thisrod-is supported on'base l0 .by means of theb aclret I55. Rocl-l56 isnot shownin the plan view, Fig. 3, but is similar to the grooved rodI53, The function ofthe rod ,I 56 is to guide the wires prop erly intothe electrolytic cell system,and for this purpose the grooves are spacedthe same as the slots in the various partitions, while the rod issupported at the correct elevation; to hold the wires at the bottom ofthe slos. v e e The grooved'rod I58, supported on bracket I51, performsa similar function at the other end of the electrolytic cell system. Therods I55 and I58 can be. supported for rotationif desired, but this isnot necessary provided they are made of some hard, smooth material. Theymay be made of glass, for example. I

-After leaving the electrolytic cell system, Figs. 2 and 3, thewiresI50- I53-passto the take-up spoolsififi lfitlz on the wire pulling.mechanism, Figs. 5 and 6, there being, however, an intervening groovedguide rod IGI, Fig. 13, which will present- 1y ;be-- described. The wirepulling'mechanisrn will be described next f ;.This,;apparatus is mountedon a metal plate I10 which rests on the base I0, and consistsessentially of two oppositely disposed rotatable cones HI and I12, amotor I19 for driving the first cone I1I, an axially movable wheel I81for coupling the two cones I1: and I12, and suitable gearing by means ofwhich the second cone I12 drives the take-up spools I55I j53eta-variable speed determinedbythe position of the coupling wheelI81. H1 I The, motor I19 maybe a split phase syn chronous motor and ismountedone. support I91 which rests on the plate I19. The motor may be.

operated on commercial alternating current, supplied Y through a switchI Sim-but preferably a standard frequency generator I is providedv torun the motor, as-zindicated in the drawing, in order toavoid speed:variations due to changes in fre quency. The motor speed maybe 1800R.JP. M. I The cone I1I may be of any suitable material, such asaluminum, for example, and is supported on a shaft I13 which isrotatable in bearings pro videdat the upper ends of the supports I15andI16. These-supports rest on and are secured to theplate 110.; The mot0rI19 drives thecone I1I by means of. a worm I89 fixed to the motor shaftand a worrn wheel I8I fixed to the shaft I13- The gear ratio may be ltov 18, for example, in which case the speed ofthecone will be 100 R. P.M. ,The cone I12 is similar to the cone HI and is mounted on a shaftI14, which is rotatable in bearings 'with which -the supports I11 andI18 ar e'provided-.;. v r e The second cone, I12 is drivenfromthe firstcone I1I" by means of an axially movable wheel I 81, as previouslymentioned. The wheellill is supported on a sliding carriercomprisingithe, two vvside members I84 and I85 which are rigidlyclamped'to the two spacers I86 and I99, the former ofwhich is drilledand tapped to receive the lead. screw I82. A tubularsleeveZBI! isrigidly secured to-the side members I84 and I85o-f the carrier, as byajdriv fit, and is slidable on the fixed shaft I83. "Ihe wheel 181 ispreferably a,

rubber tire mounted on a hub 2M which is ro! tatable. on the sleeve 2G0,suitable washers being interposed between the hub and the side members184 and I35 as indicated. The shaft l83 is secured to and supported ontwo upright standards I88 and I89 which are mounted in spaced relationon the plate III]. The lead screw I82 is provided with bearings at theupper ends of these standards, and is adapted to be rotated by means ofthe hand wheel'I9I. A' counter I90 is mounted on the standard I88, isconnected to the lead screw, and functions to 'indicate the instantposition of the carrier'onwheel I87; as measured by rotations of thelead screw.

It will be seen that by rotating the hand wheel l-9I in one directionorthe other'the carrier and the wheel I81 can be traversed ineitherdirection along the fixed shaft I83 By rotating the hand wheel ina clockwise direction, for example, the carrier can be moved to theright until the wheel I8-1- engages the cone III where it has thelargest diameter and at the sametime engages the cone I12 where it hasthe-smallest diameter. The counter I90 should be so related to the leadscrew that it reads zero in this position of the wheel I181. By rotatingthe handwheel- I9'I in the opposite direction the'carrier and the wheelI81 are: moved to the leftand the movement may be continued until thewheel I81 engages the cone II-I where ithas the smallest diameterand'cone I12. where it has the largest diameter. The reading ofthecounter at this point depends on the pitch of the lead screw. Itmay beassumed that 160 turns ofthe lead screw are required to traverse thecarrier from one extreme position tothe other. Itwillbe understoodthatthe hand wheel I91 cannot be operated unless the cones are rotating.

U The shaft Il4- on which cone I12 ismounted drives a countershaft l94-by means of;- a worm I92 and worm Wheel I93, and the said countershaftdrives the shaft 202 by means of the spur gears I95 and I96. These gearsmay be secured to their respective shafts by'means of set screws, sothat they may be changed if it should; become necessary to shift thespeed range up or "down; The shaft- I94' is rotatably mounted on asuitable support 203: V Theshaft -2 is rotatably mounted on; a, movablesupporting block; 204 so that the distance between the centers of shafts202* and I94 can be changedif made necessary bya change of gears. Thisconstruction is shown in Figs, 7 and 8"; The block 204; which" supportsshaft 202; is carried-on a support 205 to which it is; pivoted by meansof a pin 206-. The support 205 includes a vertically disposedslottedmember 2 01; The block 204 is secured inposition by means ofaclamping screw 208,- which lies in the slot in member 20-'I and isthreadedinto a tapped hole in the block 204. The clamping screw2ll8 may.conveniently be provided with a knurled head 209. It-will be seen thatwhen the screw is loosenedupthe block can-be rotated to'right or left onthe pivot pin 206, Fig. 8, and-canthen be's ecured in the desiredposition by tightening the clamping screw. g r r i The takeup spools I65I6 8 are mounted on theshaft-202 as shown. There is adisc mosecured totheshaft 282 and the spools ltd-I68 are' clamped against this discbymeans of a wing nut 2 l I. Th construction of the spools will appearclearly from Fig. '7; which shows two of "them iii-section; They may bemolded from suitableplastic material. Describing the spool I65 briefly;it has a winding space bounded by two flanges,

of which-the flange at the left is several times higher than the other.The wire being processed, such' as wire I50, is wound on from lefttoright; starting next to the higher flange, and the end- 12 .ofthe wireis attached to the spool by inserting it in a notch in the flange andbending it back. The circumference of the winding space should have someconvenient value, to facilitate relating the number of feet of wire onthe spool to the number of turns, and may be exactly one foot, forexample. The spool has to be rotatably mounted when the wire is drawnoff in the winding operation and; to this end is provided with a bearingsleeve2l 3.

The spools I65-i68 are all alike and it Will be understood that aconsiderable number of them will be provided in order topermitcontinuous operation of the apparatus. Whenfour tapered conductors havebeen made and wound on the spools I-65-I68, the spools are removed andare replaced by four empty spools.

The reference character 212 indicates a counter, which is suitablymounted on topof the block 204. -Thecounter is actuated by a pin on thegear I96, as indicated in Fig. '7, and counts the number of rotations ofthe spool's- I65-I68. Since the spools are one foot in circumference thecounter will indicate the number of feet of w re on the spools at anystage.

Eig. IS-shows thearrangement for feeding the wires onto the spoolsHit-I68 as they leave the electrolytic cells. A groovedrod I6I isprovided, and is supported on two L-sha'ped members I59 and: I60, whichare fastened to the base I0. The grooveson the rod IGI have the samespacing as the spools I65-I68; The rod I6I is axially movable. Atthestart of a processing operation, the rod is in the position in whichit is shown in the drawing, where it is held by the spring I62. As theoperation proceedsjand the wires are wound up on the spools, the rodI6'I is moved longitudinally to the right by turning the wing nut I63once me Wh le. Thus the wires are prevented from piling'up' on thespools and are wound on insingle layers. It is important that the wirebe woundon in a single layer,because it is desirable to draw the wireof? the spool inthe way that it is wound on, that is, large end first. Asingle layer also ensures that the counter 2I2 will ac,- curatelyindicate the number of feet of wire drawn through the cell system.

.It: will. be in order. now to discuss the gear ratios employedat thewire pulling mechanism, particularly-the.variable ratio between thespeeds of the cones Ill and II2, with a. view to making clear thedifferent wire speeds that may be obtained;

It has been mentioned before. that the speed of motor I19: i's.1800 R.P. M. and that the ratio of the motor speed tothat of thefirst' cone IIIis 18 ,to 1,. The speed of the cone, therefore, is R. P. M; The ratio ofthe diameter of the cone III at. its larger endftoits diameter. at thesmaller endlmay be lto 1, andsincecone I"I2= isthesame, itffollows thatWith the wheel I-8I in itsextremeright hand position (counter 190 atzero) the driving ratio between the cones is 4 to 1. Cone I-'I2-,therefore, rotates at a speed'of 400 R. P; M; As regards-the drive fromthe? cone I12" to, the; shaft, 202;, the gear ratio I92=-I931 is. 25'.to l, While-the .gear; ratio I95.-I96, is. 10 to 3 Thespeedofcountershaft I94; therefore, is 16 R". P. M. and the speed ofshaft 202- is- 4.8R'. P. Mi, or- .08-R; P. S; Now-since thecircumference'ofthe spools-carried on the shaft 202- is exactly 1' foot;the-linear speed of the wire-when it isdrawn through the electrolyticcells and wound up; on the spools will be .08 foot per second, or 12.5

13 seconds-per foot. This isthe maximum wire speed with the apparatusdescribed" The. minimum speed of the wire can be calculated in th'e'sameway from the minimum speed of the cone l12, which is 25 R. P. M.,andxturns out-to be .005. foot per second, or 200 seconds per foot. Thatthe minimum speed of cone H2 is 25 R. P. M. will be clear from .the factthat with the drive wheel l81in its extreme left hand position (counterI90 reading 160) the driving ratio between cones will be 1 to. 4.

The calculation of the wire speeds for inter.- mediate settings of thelead screw is somewhat more complicated. The equation for determiningthe speed of cone I12 for any speed of cone Ill and any setting of thelead screws is-- 's' =s in which S=speed of cone I12 S =speed of coneI'll j d=diameter of cone IH at the pointof drive d"=diameter of cone H2at the point of drive for a few intermediate settings of the lead screware given in the table below. From the cone speeds the wirespeedsfor thesame lead screw settings can be calculated and' such values are alsoincluded in the table.

Lead Screw Setting The above table is incomplete, but will suffice forthe purposes of this explanation; A complete tableor chart may beprepared on the same plan, showing the wire speeds in seconds per footfor all the lead screw settings from 0 to 160, inelusive. This table maybe used in determining the proper lead screw settings which are'required to produce any desired speeds, as will shortly be more fullyexplained.

It should be noted that although the values given for the conespeeds'and wire speeds are theoretically correct, the actual values maydiffer slightly, due to the fact that the drive wheel I81 between thetwo cones must have an appreciable width and that the point of drivedoes not always coincide with the exact center ofthe wheel. This maycause slight variations in thevalues of d and d for any particularleadscrew setting. These variations seem to average out to some extentand are not serious. It may be stated that a table of wire speedsprepared by timing with a stop watch checks quite closely with the tableprepared from the calculated values.

If desired a curve may be prepared in which the wire speed may readilybe determined.

The electrolyte used is a mixture of ortho. phos.

phoric acid and. sulphuric acid and preferably has the followingcomposition: I

. Parts H3PO'4; 300

H2804 60 E20 n 60 In the above formula, the proportions are. given byvolume. The sulphuric acid is concentrated, while the phosphoric acid,is concentrated, that is, it contains 15% of water.

i The quantity of electrolyte should be relatively large as compared tothe capacity of the electro.- 'lytic cells. For the apparatus shown thecirculat ing system should hold fivefgallOHS or more. of electrolyte.

Generally speaking, the invention is adapted for the processing of anykind. of wire..although the'electrolyte might have to be modified in.certain cases. When liquid mercury is used, for making the electricalconnections, to the wires,

however, as in the apparatus disclosed. herein,

only wire which does not amalgamate' readily can be used. That is, thecomposition of the wire must be such that it is not wet by the mercury.Fortunately for the 'manufacture .of rheostats and potentiometerssuitable. resistance wire which is not readily attacked by mercury isavailable. The resistance wire known as Nichrome may be used, forexample. Another resistance wire which has been used successfully hasthe follow ing composition:

Nickel d5. percent.

Chromium 9. percent Manganese .1 1.6 percent Silicon 1 percent Carbon.04 to .1 percent Iron the balance Resistance wire of the abovecomposition has a specific resistivity of about 600 ohms per circularmil foot, has a low temperature coefficient, and a. fairly high tensilestrength.

' The apparatus described, with 12 mil slots, will handle wire up toabout 10 mils in diameter. The slots could be made larger to take largerwire, but there is a limit in this direction imposedb'y the excessiveleakage of water and electrolyte that would occur. The necessity ofavoiding loss of mercury also imposes a limit on the size of the slots.

Before processing, the wire should be given a treatment known asdepassivation, the object of which is to prepare the wire for the anodictreatment in the electrolytic cells. Unless the wire is depassivated theanodic reaction does not start promptly atall points on the surface ofthe wire when current is applied, and somewhat irregular and uncertainresults are obtained.

In order to facilitate the depassivation treatment the wire should bewound on the spools such as I43, in spaced coils, with the coils inadjacent layers crossing each other in a kind of basket weave pattern,thus producing an open winding which is readily penetrated by thedepassivating agent. The spools such as I43 should have ribbed or flutedwinding spaces and should be made of material which is not attacked byacids. 7 r v The spools carrying the wire to be depassivated are firstdipped in a cleaning solution such as is treatment.

. as commonly usedin electroplating processes, in order .to make thewire chemically clean. The wireis then rinsed in water and is given acyanide dip inorder to remove any traces of the chemical cleanerj thatmay remain. .After rinsing once more, the wire is immersed inhydrochloric acid for about thirty seconds and is then rinsed and dried.This completes the depassivation The treatment is efiective for only a;day or two and consequently the wire should not be depassivated .untilshortly before it is to be used, preferably on the same day, or the daybefore. I

The operation of the apparatus in the manufacture of tapered conductorsmay now be explained. For thispurpose it will be assumed that theapparatus is installed as described, and is to be started'up for thefirst time, or is being started up after a shut down.

The main tank 'I3is1first filled with electrolyte of the hereinbeforestated composition; The electrolyte should almost completely fill thetank, as the loss of electrolyte to the rest of the system when thecirculation is started will reduce the electrolyte in the tank to a safeworking level, as indicated by the dotted line.

'j .The switch H9 is now closed in order to start thefm otor 84, whichdrives the pump 83. The operation of the pump transfers electrolyte fromthefjmain tank 13 to the' auxiliary tank 8! through the hose connection85; The electrolyte in tank '81 immediately starts to drain out by wayof the hose connection 93 to the cathode sections of the electrolyticcells, filling all the compartments such as 24, Fig. 10, withelectrolyte up to the tops of the overflow tubes such as 39 and 40, Aselectrolyte continues to be supplied it overfiows through the tubes suchas 39 and 40 in each cathode compartment and is collected in the trough9H,;whence it returns to the main tank 13 by way of the hose connectionIGI. Thus the circulation; of electrolyte through the cathodecompartments of the electrolytic cells is established and maintained. I

I The pump supplies electrolyte to the auxiliary tank 8| faster than itcan circulate through the electrolytic cells and theta'nk soon fills,therefore, the excess draining'ofi through the overflow pipe 86 and hoseconnections '81 and 89 to the vessel 98, containing the hydrometer 90,which is also filled and drains into the main tank 'I3b'y way of thehose connection 9|.

The wash water may now be turnedon by opening'thevalve I65,which'supplies water to the pipe [03,? which in turn supplies water tothe nozzles such as 19'! and I68. Each nozzle directs a stream of wateronto the me'rcury'in the 3550-. ciated mercury compartment such as 59,Fig. 10, and fills the compartment, the water overflowing the partitionsuch] as 58 to the washing compartment such as 56, whence it overflowsthrough a pipe such as 51 to the collection trough 9'1. From thecollecting troughthe water isallowed to run to waste through the hoseconnection [52.

. As mentioned before, there is some leakage of electrolyte through theslots such as 2'! and 28 in the walls of the cathode compartments andthere is also a leakage of water through the slots in the partitionssuch as and B2. The leakage'electrolyte is collected inthe compartmentssuch as 48 and 69, whence it drains into the collecting trough 98, whilethe leakage wateris collected in the compartments such as 52 and B1,whence it drains into the collecting trough 91. Thus the electrolyte andwash water circulating systems Ill 116 are kept/entirely separate,notwithstanding the fact that they both-leak.v v

The next operation is to turn on the supply of cooling water to the maintank. i3 at valve H3. The switch I29 in the circuit oftheelectromagnetic valve Il2 can be. closed at thistime also. The valveremains closed, however, for its circuit is open at contacts of therelay H3. No' cooling water is supplied to thetank, therefore, for thepresent. 1

When the switch H 9 was'closed it completed a circuit for theelectromagnetic valve and this valve accordingly opened. The gas.may,ttherefore, be turned on at valve 15} and the burner. H maybelighted. The heating of the electrolyte in the main tank T3 isthusstarted. The gas may be turned on full. at the start in order to lose aslittle time as possible.

When the temperature of the electrolyte reaches about 46 C. the gassupply. to the burner 11 is adjusted so that only a slight amountofexcess heat is supplied to the tank. The heat supplied must besufficient to produce a rise in the temperature of the electrolyte, butat a slowrate,

so as to avoid waste-of gas. j

The thermal switch 1 i5 is set to close at 47? .C. When the temperatureof the electrolytereaches this value, therefore, the switch operates andcloses a circuit for relay H3. Upon. energizing, relay H3 closes acircuit for the electromagnetic valve H2, which now opens and admitscooling water to the coil H0 in the main tank 13. This stops the rise inthe temperature of theelectrolyte, which shortly begins to cool. Theswitch IIG then opens, relayl-l3 is deenergized, and the valve H2 isclosed. The cooling operation as described above is repeated as often asrequired, depending largely upon the'adjustment of the burner TI, andthe arrangement is effective to maintain the temperature of theelectrolyte within close limits.

The system will operate with the electrolyte at other temperatures thanthe one given above, provided the temperature is maintained constant.The reason why a variation in temperature is objectionable is thatanodic reduction like electro plating, effects a smaller actual transferof 'metal than might be expected from theoretical calculation. In otherwords, the anode current efiiciency is considerable less than 100%. Theeiliciency changes with changes in temperature, and; therefore, thetemperature should be kept constant in order to eliminate this variablefactor that would otherwise be present. Since the anode currenteificiency,increases with an increase in temperature, it is desirable tooperate at a fairly high temperature. If the temperature is too high,however, disadvantages. appear, such as excessive loss of water byevaporation. It has beenfound that very satisfactory results are securedif the temperature is maintained constant at some value which is about46 C. or 47 C.

The .density of theelectrolyte should now be checked by meansof thehydrometer Itis found that good results are obtained. if the spe-. cificgravity is maintained at about 1.600. t The specific gravity isimportant as affecting the finish on the processed wire, a bright,smooth finish being obtained only if the specific gravity is maintainedwithin a certain range. This range appears to have wider limits withhigher temperatures, which is another reason for operating with theelectrolyte at a fairly high temperature. So far as thefnish isconcerned, therefore, some variation from the stated value of 1.600would be permissible, but the specific gravity also affects the anodecurrent efficiency and hence should be held as close as possible to thevalue selected. The principal change that occurs in the specific gravityis due to the loss of water by evaporation. The hydrometer should beobserved frequently and water added when required.

The operator may now close the switch I98, Fig. 6, to start the motor II9. The cones III and I72 are thus set in rotation and the hand wheelI9I may be rotated to set the counter I90 to zero. This operation movesthe drive wheel I8! to its extreme right hand position, in which thecone II2 rotates at maximum speed. The switch I98 is now opened to stopthe motor I79.

If not already done, four take-up spools such as Ie65-I68 may now beplaced on the shaft 202, where they are clamped in position by means ofthe wing nut 2 I I, as shown in Fig. 6.

Four spools such as I40-I43 containing depassivated wire may now bemounted as shown in Fig. 2. The end of wire I50 is then passed under thegrooved rods I56 and I58, Fig. 2, and

the grooved rod I6I, Fig. 13, and is attached to the high left handflange on the take-up spool I65, Figs, 6 and 13. The portion of the Wirewhich extends between the grooved rods I56 and I58 may simply rest ontop of the electrolytic cells for the present. The other wires I5I, I 52and I53 are attached to spools I66, I61 and I68, respectively, in thesame manner.

The operator should now adjust the wires prop erly in their respectivegrooves in the rods I56; I58 and I6I, and will then see to it that thewires enter their respective slots in the various partitions andcompartment walls of the electrolytic cell system. The Wires may beguided into their slots and pressed down by hand and will readily fallinto the proper positions. The relation of the wires to the other partsof the electrolytic cell systemmay be seen from Fig. 2, and also fromFig. 10, which shows the portion of wire I52 which extends through theanode section I8 and cathode section I9. All four wires are also seen inthe plan view Fig. 3, except that they are not visible in the mercurycompartments such as 59 nor in the cathode compartments such as 24,being immersed in the mercury and electrolyte which is contained inthese compartments.

It will be seen that the wires extend through the electrolytic cellsystem on straight lines from the guide rod I56 to the guide rod I58.The force required to pull them through the cells is, therefore, verysmall, as previously mentioned. In fact, practically the only forcerequired is that which is necessary to overcome the friction at thebrakes on the spools hill-I43. The brake friction should be justsufficient to keep the Wires taut.

The motor generator set which includes the D. C. generator I may now bestarted, and as soon as the generator Voltage is built up, the switchI34 may be closed to its upper position. The resistances I32 and I33constitute an artificial load which has previously been adjusted to takeapproximately the same current as the electrolytic cell system. Enoughof the current regulating devices such as I26 are now out in by means ofswitches such as I21 to pass the desired amount of current, which in thecase of the apparatus described herein, with four wires being processedsimultaneously, is about 13 amperes. An accurate adjustment of thecurrent can be made by means of the high shunt resistance I29 and therheostat I30.

The factors having a bearing on the selection of the proper currentvalue may be discussed briefly at this point.

The current density, referring to the current density at the anodes inthe electrolytic cells, which are constituted by the wires beingprocessed, should be as high as possible. One obvious reason for this isthat the higher the current density the faster the anodic reduction.Another reason is that a fairly high current density is necessary inorder to secure a bright, smooth finish on the wire. The current densityis limited by the current carrying capacity of the wires, however, andshould not be so high as to unduly heat the wires, which are in contactwith the cell walls and partitions at the slots. The polystyrene ofwhich the parts are made becomes soft at a rather loW temperature.

Now the characteristic of a wire which determines-the current density isits surface area,

whereas the current carrying capacity or conductivity is determined byits cross section, other things being equal. Since as we increase thesize of the wire the cross section increases faster than the surfacearea, the larger the wire the higher the permissible current density.

The current value of 13 amperes is a value which has been foundexperimentally to be satisfactory in the described apparatus forprocessing of fine wires, the smallest diameter of which is on the orderof 1 mil. This amount of current does not raise the temperature of thewires beyond a safe point and at the same time it results in asufiicient anode current density to give a bright, smooth finish onwires up to 4 or 5 mils in diameter, or slightly larger.

It will be appreciated, however, that as the size 'of the wire isincreased the current density will decrease, with the same totalcurrent, and will eventually become'so low as to affect the finish onthe wire. For wires having a larger minimum diameter than about 2 or 3mils a considerably higher current value could be selected, and may berequired. Whatever value is selected it should be kept constant, ifwires having a desired predetermined taper are to be made. It should beborne in mind that in this discussion reference is being made to theapparatus disclosed, comprising sixteen cathode compartments and adaptedto process four wires simultaneously. If the number of cells isincreased, or the number of wires, the total current must be increasedin proportion in order to obtain the same current density.

The statement that the current should be kept constant, of course, is inconformity with the preferred method of operation, in which all factorsaffecting the rate of anodic reduction are kept constant, except thetime. By varying only the time factor the method is simplified and hasbeen found to be suitable for the production of a considerable varietyof tapers. It is recognized, however, that two or more different currentvalues could be used, each on a different section of the wire, and eachbeing kept constant while it is in use. For example, a current value of25 amperes could be used on the larger half of the wire and a currentvalue of 13 amperes on the smaller half. This procedure would complicatethe process somewhat, but it would speed it up, and might be necessaryin certain cases to give sufiicient current density to produce a brighfinish at the large end of the wire.

Continuing with the description, the apparatus is now ready for theprocessing of the four wires l9 7 ESQ-K53 whichhave been connected up,it being assumed that sufficient time has elapsed since the switching onof the artificial load to permit thecurrent regulating devices lit towarm 7 up and attain a constant current carrying capacity. The operatormay accordingly throw the s'witch E3 to its lower position, therebydisconnecting the generator 525 from the artificial load and connectingit to the bus bars l2! and i 22 of the electrolytic cell system.

Current now starts to flow through the electrolytic cells and the anodicreduction of-the wires begins. At thistime the operator also closes theswitch I93 to start the motor 519, thus setting the spools [55468 inrotation and beginning to pull the wires 150453 through the electrolyticcell system by winding them up on the spools. The counter ESQ havingbeen set at zero, the the linear wire speedis 12.5 seconds per foot.

The electrolytic cell system. is approximately seven feet long,measuring from the point where the wires enter the first cathode sectionto the point where they leave the last cathode section,

and accordingly it takes8'7.5 seconds (7 l2.5)

for the seven foot sections of wire which were in the electrolytic cellsystem at the start of the operation to be pulled entirely through. Itwill be assumed now that the operator allows a few more feet of thewires to be pulled through and then stops the operation by switching thegenerator I back on to the artificial load and by stopping the motor'Fit. The operator can tell when to do this by observing the counter 2l2,which preferably was set-to zero beforemot-or M9 was started.

It should be stated that the foregoing assumption as to the procedurefollowed by the operator is based on the further assumption that theoperator has no information as to the constants of the apparatus; thatis, he does not know the wire speed which is required in order toproduce the desired taper on the wires. He will naturally have toinvestigate this phase of the matter before he is able to produce anycomplete tapered wires having desired characteristics as to length andrate of taper. The resistance wires under consideration may be anywherefrom 30 to 100 feet long, or many times longer than the electro- 1yuc'cell system.

The wire 153 may now be cut off where it leaves the electrolytic cellsystem, and the winding thereof on the spool H58 is completed by hand,the end being attached to the spool in any suitable manner, with a pieceof tape, for example, or by engaging it in a notch in the right handflange of the spool. This spool is then removed. The other wires I52-l5B are then out on one after the other, the unwound portions are woundup on their respective spools, the ends are attached to the spools toprevent unwinding, and the spools are successively removed.

We now have four test wires, each about ifteen or twenty feet long,which have been processed as described and wound up on individualspools. Each of these wires includes three parts, a section which wasbeyond the electrolytic cell system and attached to the associatedtake-up spool when the operation started, a seven foot section which wasin the electrolytic cell system when the operation started, and whichhas been drawn out, and a third section which has been drawn in and outof the electrolytic cell system, or entirely through it.

Before explaining how these test wires are used, it will be advisable togo over the operation again and consider more in detail how it hasaffected the three sections above referred to. 7

Considering wire 153, for example, the first section thereof whichextended between the electrolytic cell system and the take-up spool isobviously unafiected by the operation, being merely wound up on thespool.

The next section, the seven foot section, is in the electrolytic cellsystem when the operation starts, and successive portions of it fromright to left are subjected for progressively longer times to the actionof the electrolyte as the section is drawn out. It is to be expected,therefore, that this seven foot section will be tapered from theoriginal diameter at the right to a smaller d."- ameter at the left.

In order to explain more in detail the nature of the taper and how it isproduced, the seven foot section may be considered as being made up ofsub-sections 1,3, 5, '7, etc., which werev in the cathode sections atthe time of operation was started, and sub-sections 2, 4, 6, etc., whichwere located in the contact selections at that time. The :sub-sectionsare numbered from, right .to left, as the apparatus appears in Fig.2.

Let us first consider'the effect that is produced on the wire by itsmotion to the right for a distanc'e'suflioient to pull the odd numberedsubsections of the wire, which were located'in the cathode sections atthe start, entirely out of such sub-sections. This distance isapproximately 2 inches in the apparatus shown here- Sub-section No. 1was in the last cathode section 22, and is progressively reduced indiameter from right to left, as it is drawn out of the cathode section.That this is true will be evident from the fact that successive parts ofthe Wire from right to left are subjected for progressively longer timesto the action of the electrolyte.

Simultaneously with the tapering of sub-section No. 1, as describedabove identical. tapers are produced at all the other odd numberedsubsections as the result of their being pulled out of their respectivecathode sections.

The movement of the wire which was sufficient to pull the No., lsub-section out of the last cathode section was, of course, effective topull an equivalent length of the No. 2 sub-section into such cathodesection, producing a taper which is complementary to that produced onthe No. l sub-section... That is, the taper is reversed. I

The same effect is produced at all the other even numbered sub-sections,4, 6, etc., as they are drawn into the associated cathode sections nextadjacent on the right. Each such even numbered sub-section is given areverse taper.

The contact sections are somewhat longer than the cathode sections, thatis, the space between two cathode compartments is somewhat longer thanthe length of a compartment, and consequently'at this time there willbev a portion of the No. 2 sub-section which has not yet' entered theassociated cathode section. The same is true of the other even numberedsub-sections.

Consider now the effect after the wire has moved, to the rights. littlefarther, or just sufficient to cause the left hand end of the No. 2sub-section to enter the cathodesection. This movement of the wirecauses a part of the No. 2 sub-section to pass out of the cathodesection, and is effective to move the taper along the wire from right toleft, the part of the sub-section which passes out of the cathodesection being 21 reduced to a cylindrical formation. Again the effect isthe same at the othereven numbered sub-sections.

We may next consider the effect which is produced by the furthermovement of the wire to the right far enough to pull the No. 2sub-section entirely out of'the last c'athode'section 22, such movementcausingthe No; 3sub- -section to be drawn into said Icathode section.The No. IZ'ESllbsection has its contour changed to that of a cylinderthroughout its length; for it hasbeen pulled entirely through thecathode section and all points on its surface have been subjected to theaction of the electrolyte for equal periods of time. The No. 3sub-section, which was tapered by being drawn out of the cathode sectionin which it was locatedat the start, is reduced to a cylinder also, forthe effect produced-by pulling it out of onecathode section and intoanother is the same as that produced'by pulling it into and out of thesame cathode section. 1

It Will be clear that the efiectproduced on the remaining odd numberedsub-sections" is the same; that is, these sub-sections are'all reducedto cylinders. Since the even numbered subsections also have acylindrical formation at this time, the entire seven foot section we areconsidering, or rather that part of it which still remains in theelectroyltic cell system,- will be cylindrical in form; as it was beforetheoperation started. Its diameter has been reduced,

however.

We may consider next the result which is :produced by thefurther'movement' of the wire to the right far enough to entirelywithdraw theiNo.

3 sub-section from the: last cathode section'22, such movement.al'socausing'the" No. 4 sub-section to enter the cathode section:

From what has already been said it will be clear that the No. 3sub-section is'taperedias it is drawn out of the cathode section;'Th'e'taper is similar to that which was produced on subsection No. 1,but it will be understoodxthat' the largest'diameter of the taperedsub-section No. 3 is the same as the smallest diameter of taperedsub-section No. 1, these sub-sections being connected by the cylindricalsub sectionfNo. '2.

It will be unnecessary to continue farther with this detailed analysis.It will 'be'clearthat' the complete seven foot section of wire, afterithas been drawn entirely out of the electrolytic cell system, will bemade up of sixteen taperedisubsections, or the same 'number'ofsub-sections'as there are cathode sections, and fifteen'cylindri calsub-sections. The first taperedsub section' will have its largestdiameter equal to that ofthe unprocessed Wire, and each of theremainingtapered sub-sections will have .a larger 'diameter which isequalto the smaller diameter of the next tapered sub-section totherigl'it. The cylindrical subsections: which join the taperedsub-sections will progressively decrease in diameter from right to left.

For practical purposes these cylindrical subsections may be'neglectedand the seven foot section may be considered as having acontinuioustaper from one end .to the other. .As a matter of fact the number ofsub-sections great enough so that the points where the contour of thewire changes from tapered to cylindrical can scarcely be detected.

As regards the'remainder of Wire 153, the section-which is pulledthrough the-electrolytic cell system following the seven foot section;it will be clear that this third section will have the form of acylinder, the diameter ofwhich-is equal to the-smaller diameter of thetapered seven foot section. That this is true'will be evident fromthefact that all parts of the third section: are pulled entirely throughthe electrolytic cell system and are subject to the action of theelectrolyte for equal periods of time.

The test wire I53 as thus produced, therefore, comprises-an end sectionseveral feet long, which has not been subjected to'the-action of theelectrolyte and which has its original diameter, a middle section sevenfeet long which may be regarded as being continuously tapered, andanother untapered or cylindrical end section several feetlong which isof 'reduced'diameter. v

The operator may now proceed to ascertain the diameter of the seven foottapered section of wire I53 at its smaller end. The diameter at theother end, of course, is that of the original wire, which presumably isknown. The smaller diameter is equal to the diameter of the smaller endsection and is determined in any suitable manner. One method which iswell adapted for use in connection with these small resistance wires isto measure the resistance of a carefully measured length of the endsection and calculate the diameter from the result obtained and theknown resistance of the material per circular mil foot.

Measurements may be made on the other three test wires in the same way.The results should be the same, or approximately the same. If thediameters thus determined are not substantially the same, the reason forthe discrepancy should, of course, be found and corrected and additionaltest wires should be prepared. Improper depassivation might be thesource of trouble. Assuming that the results on the four wires check,the average of the four diameters thus determined may be taken as thetrue diameter.

From this point on it will be convenient to continue the explanationwith reference to Fig. 15, which illustrates the method of producing aresistance wire comprising a cylindrical end section having a diameterof d1, a tapered section 21 feet long having a diameter d1 at one endand a diameter d4 at the other end, and another cylindrical end sectionhaving a diameter d4. It will be assumed that this is the particularresistance wire that is to be made. The drawing also shows one of thetest wires in superimposed relation, 'comprisingra tapered section 7feet long and the two cylindrical end sections as shown. As to this testwire, it will be assumed that the diameter of the tapered section at thesmaller end, as determined by the measurements just described, is d5.

A little consideration now will show that the test wire is notsufficiently tapered. Its diameter at the left hand end of the taperedsection is d5, whereas the diameter of the desired resistance wire atthe corresponding point is d2. The operator accordingly is advised thatthe time occupied in producing the tapered section of the test wire wasinsufficient. That is, the wire was drawn out of the electrolytic cellsystem in too short a time for the requisite amount of metal to beremoved. 'Theco rrect time can be determined by comparison of the volumeof metal actua'lly'removed with the volume of metal which has to beremoved in order to produce the required taper, the volume of metalremoved being directly proportional to the time.

Suppose we let V0 bethe volume of metal removed from theseven foottapered section of the test wire to reduce its diameter at the small umeV2,

end to d5, and let V1 represent the volume of metal which must beremoved inorder to. re-.

The time to being known, and likewise the volumes. V and V1, we cansubstitute the actual values and solve for t1, thus obtaining the actualvalue of ii in seconds. i

The operator can make some further calculations at this point, whichshould enable him to go ahead with the production of four resistancwires having the desired taper.

In order to explain this, reference may be made to Fig. again, whichshows the contour of one of the desired resistance wires, andconsideration may be given to what further information will have to beobtained in order to carry out the operation successfully.

The resistance wire as depicted in Fig. 15 has a tapered portion whichis 21 feet long, consisting of three seven foot sections, indicatedassections I,2and3.

Section I is the section that is in the electrolytic cell system whenthe operation starts. From the calculation already made it has beendetermined that if this section is pulled out in time 251 the desiredtaper will be produced, that is, the tapered section will have a largerdiameter equal to 11 and a smaller diameter equal to d2.

When section I is pulled out of the electrolytic cell system, section 2is pulled in and will become tapered as indicated by the dotted lines300. If section 2 is now drawn out at the same wire speed its contourwill be reduced to that of a cylinder as indicated by the dotted lines39!. Section 2 should not be cylindrical, however, but should be taperedfrom a large diameter of d2 to a smaller diameter of 013. It will beevident that in order to produce this taper an additional volume ofmetal equal to V2 will have to be removed.

Volume V2 can be calculated, like volume V1 was calculated, and will beslightly smaller than the latter volume. Time t1, or the time requiredto remove volume V1, has already been calculated. Then if i2 is the timerequired to remove vol- Substituting the known values and solving fort2, the time in seconds may be obtained as in the case of ii.

We may now let T1 equal the total time required to pull out section Iand T2 the total time required to pull out section 2. Then it will beevident that the following are true:

Suppose now that section 2 has been pulled out of the electrolytic cellsystem in time T2 and has been tapered from the larger diameter of 012down to the smaller diameter of (23. At the same time, section 3 wasdrawn into the electrolytic cell system and was tapered as indicated bythe dotted lines 302. Now if section 3 is pulled out of the electrolyticcell system in the same time that was spent in drawing it in, that is,in time 24. T2, it will be evident that a cylindrical contour willresult, as indicated by the dotted'lines 363; and it will be obviousthat if the desired taper is to be produced a further volume or" metalV3 will have to be removed. The time required to remove this additionalvolume of metal may be represented by ts, which can be computed in thesame way that time t2 was'computed.

We may now let T3 represent the total time required to elapse in pullingout section 3, and can write the equation The operator may now refer tothe table or curve which shows the relation between the wire speeds andlead screw settings and the lead screw settings corresponding to thewire speeds S1, S2, and S3 may be determined and noted down.

Having completed the calculations described in the foregoing, theoperator is now ready to proceed.

. The first thing to do is to start the motor H9 to set the cones Ill,and H2 in rotation. The hand wheel l9! may now be rotated in order togive the lead screw I82 the proper setting to produce a wire speed equalto S1. The correct setting has previously been determined, as explained,and is made by turning the hand wheel until the counter I shows theproper number of turns. The lead screw setting having been completed,the operator will stop the motor I19.

Four empty take-up spools such as SE-I 58 may now be placed on the shaft292, where they are secured in place by the wing nut. The counter H2 isset to zero.

The operator may then out off the wires 150-! 53 just to the left of thepoint where they enterthe electrolytic cell system. The parts of thewires which have been drawn into the electrolytic cell system are liftedout and discarded. The ends of the wires on spools l lo-M3 are thenpassed beneath the guide rods and are attached to the take-up spools aspreviously described. As before, the wires are properly located in thegrooves of the guide rods and are pushed down into the slots in the cellpartitions.

Everything being ready now, and the operator having checked the currentto make sure it is the same as before, the switch I 34 is again thrownto its lower position. The generator is thus again connected to the busbars 12! and I22 and current starts to flow through the electrolyticcell system. The switch I98 is also closed at this time, starting motorI19, and initiating the rotation of the take-up spools to pull the fourwires through the electrolytic cell system. v

One of these wires may be assumed to be the wire shown in Fig. 15.Section I of this wire is the section which is located in theelectrolytic cell system at the start and is pulled out at a speed whichis equal to S1, calculated as previously described. It follows,therefore, that the section is drawn out in time T1 and will becometapered from a diameter of d1 at the larger end to a diameter of d2 atthe smaller end.

As the operation proceeds the counter 2I2 counts the number of rotationsof the take-up spools and indicates the number of feet of wire drawn outof the electrolytic'cell system at any instant. The operator watches thecounter 212 and as soon as section I has been entirely drawn out, asindicated by the counter, he quickly changes the lead screw setting tothe previously notedsetting which corresponds to wire speed $2. This canbe done in a couple of seconds and istimed as accurately as possible tocoincide with the time the end of section I leaves the last electrolyticcell. I

Section 2 is now pulled out of the electrolytic cell system at the wirespeed S2, and in time T2, whereby it is tapered from the diameter of (laat the larger end to the diameter of 113 at the smaller end.

As the end of section 2 leaves the electrolytic cell system the operatorquickly changes the lead screw setting again, this time to thepreviously noted setting which corresponds to the wire speed Section '3is accordingly drawn out of the electrolytic cell system at, the wirespeed S3, and in time T3, and is tapered from .the diameter of da at the.larger end to the diameter of di at the smaller end.

. When the end of section 3'yleaves the electrolytic cell system theoperator will note the fact, counter 2|2 indicating that 21 feet of wirehave been drawn out, but makes no further change in the. wire speed. Thewire continues to be pulled out at the speed S3, therefore, and acylindrical end section is formed having the diameter (14.

When this end section is long enough the operatorwill stop the operationby reversing switch I34 and opening switch I98.

The four wires are now cutoff just to the right of the electrolytic cellsystem, the unwound portions are wound up on the respective take-upspools and the spools are removed all as previously described. F

-Four tapered wires have now been produced,

each comprising a cylindrical end section having a diameter of (ii, asection 21 feet long which tapersfrom a diameter of (11 at the largerend to a diameter of (14 at the smaller end, and 2. cylindrical endsection having a diameter of (14. These wires should conform tospecifications, provided the operations have been carried out asdescribed.

The operator. may proceed now to make four more tapered resistance wiresin the same man- 1161'. In this connection it should be noted that thelead screw setting must be changed first to the proper settingcorresponding to speed S1, since the cones Ill and H2 have to be inrotation when the change is made. It should be noted also that thesections of wire which were in the electrolytic 'cell'system when thepreceding four wires were completed have to be cut off and discarded, ifthe described procedure is followed.

.The treatment of the tapering theory in the foregoingexplanationhasbeen general, with a view to promoting. an understandingof how the taper is produced, and the principles involved inpredetermining the wirespeeds and lead screw settings which arenecessary :to. produce such tapersasmaybe required.

' Inthis connection it willhbe understood that the directions'given. areapplicableto any size of wire within the capacity of the apparatus, the:wire size being limited only. by the size of the slots. With 12milslots wire up to about mils in diameter may be handled, and the sizeof the slots could be increased somewhat. It will be understood alsothat the-directions are applicable to the manufactureof resistance wiresof any desired. length, although the length should be wires the slope ofthe taper is correspondingly reduced.-

As regards the form of the taper it will be evident from an inspectionof Fig. 14 that the taper there shown is a conical or straight linetaper,

when considered from the standpoint of the decreasing wire diameters d1,d2, daand (14. In

other words, a curve constructed by plotting the successively decreasingsection end diameters against the corresponding distances measured alongthe wire is a straight line. The case is different if considered fromthe standpoint of the decreasing cross-section of the wire, since thecross-section at any point is proportionate to the square of thediameter at that point. A curve constructed by plotting successivelydecreasing cross-sections against the corresponding distances is anexponential curve defined by an equation of the second order. 7

In the manufacture of tapered wires for potentiometers the resistancecurve is of primary interest. Since the resistance of a wire is directlyproportionate to its cross-section, the resistance curve will be of thesame type as the cross-section curve. Hence the resistance curve of thetapered wire shown in Fig. 14 will be a second order or square curve.

If it is desired to make a resistance wire having a straight lineresistance curve, then the crosssections at the ends of the seven footsections can be computed from the resistance curve and from the valuesthus obtained the corresponding diameters can be calculated. Thesediameters can then be used to calculate the wire speeds in the manneralready explained. Following the same procedure resistance wires havingother types of resistance curves can be made.

In order to give a more definite idea of what may be expected in thepractice of the invention, especially as to the time values involved,the data used in the manufacture of a representative resistance wirewith the apparatus disclosed herein will now be given.

The resistance wire selected for this purpose is made of the alloypreviously referred to herein and has an overall length of about 49 or50 feet,

The table below gives the data for the manuf acturc of the above Wire,it being understood that four wires are made at the same time, and thatthe values for total current, electrolyte density and electrolytetemperature are as previously recommended herein.

Section 'In the above table the meaning of the entries in the first twocolumns will be obvious. The values of T given in the third column arein seconds and are calculated as already explained. Each entry in thiscolumn shows the total time T that should elapse While the correspondingsection is being drawn outof the electrolytic cell system. The values ofS in the fourth column are the wire speeds in seconds per foot and areobtained by dividing the corresponding values of T by '7. The values ofL in the fifth column are the lead screw settings in turns, as indicatedby the counter, and are obtained from a curve such as has beenpreviously mentioned, which was, made by plotting the lead screwsettings against the corresponding wire speeds.

In the manufacture of the wire the operator makes use of only theentries in the last column. Theinitial lead screw setting is 49, andaccordingly section I of the wire is pulled out of the electrolytic cellsystem at a wire speed of 28.8 seconds per foot and ina total time of201.88 seconds. The operator keeps track of the sections by means of thecounter 212 and as the end of the first section leaves the electrolyticcell system, or isabout to leave, he changes the lead screw setting from49 to 86, with the result that section 2 is pulled out at a wire speedof 54.8 seconds per foot and in a total time of 383.57 seconds. Theoperation proceeds in this manner, with lead screw settings of 105, 119and 128 as sections 3, 4 and 5, respectively, are pulled out. The lastlead screw setting remains unchanged while the cylindrical section atthe end is pulled out. The end sections are not shown in the table.

The total time required in the electrolytic cell system may be found byadding up the values of T in column 3 of the table, including anadditional entry equal to the last entry to take care of the smaller endsection, and will be found to be a little more than 57 minutes. The timerequired for other resistance wires is in proportion to the amount ofmetal that has to be removed.

The output of the apparatus in making this specific resistance wire isabout four wires per hour. The output can readily be increased byincreasing the capacity of the machine, which can easily be arranged tohandle more wires at a time.

While the procedure explained in the foregoing gives excellent results,a possible objection, if it can be referred to as such, is that theaccurate timing of the changes in lead screw settings is interferredwith to some extent by the impossibility of making such changesinstantaneously. The time required to make a change is very small incomparison with the time required to pull a seven foot section throughthe electrolytic cells, andconsequently the operation is not critical,but a chance for some slight irregularity does exist, especially if thechanges in lead screw settings are made manually as described.

A procedure which may be adopted to facilitate timing and to minimizethe efiect of an occasional inaccuracy consists in making the firstchange in the lead screw setting after six feet of wire have been pulledout and in changing the setting every three feet thereafter, the changesbeing proportionately smaller than those which would be required if madeonly every seven feet. This procedure has been used successfully on anumber of diiferent resistance Wires. The first change is started alittle in advance and the other changes are rather small and can be madevery quickly.

There are other reasons which may make more frequent changes in leadscrew settings desirable. When the setting is changed once per section,the apparatus inherently turns out seven foot sections each having astraight line resistance curve, which is eminently suited to themanufacture of multisection wires having the same type of resistancecurve. This characteristic of the apparatus, however, makes it somewhatless suitable for the manufacture of resistance wires having a conicaltaper or resistance wires having resistance curves Which are notstraight lines. This is not to say that satisfactory wires having suchtapers cannot be made in this way, for the taper is corrected everyseven feet and the departure within each section is generally too smallto be material, especially if the wire contains a considerable number ofsections. In case it should be desired to modify the normal taper in thesections to make it conform more closely to some desired over all taper,it can be done by introducing appropriate changes in the lead screwsettings.

In referring to lead screw settings here and elsewhere, we have in mindthe particular wire pulling mechanism which is shown and describedherein. It will be understood, however, that any other suitable wirepulling mechanisms can be used, so long as it includes some device bymeans of which different wire speeds may be obtained as required.

The electrolytic cell system has been fully described and a certainamount of explanation as to its operation has been made- A fewsupplementary remarks may be helpful nevertheless. 7

Referring to Fig. 10, when the wire I52 leaves the cathode section 11,it pulls a certain amount of electrolyte along which drains intocompartment 48. The wire is wet with the electrolyte, however, as itenters the washing compartment 55. Here the electrolyte is thoroughlywashed off, a good circulation of wash water being maintained. The wateralso Wets the wire but is squeezed off as the wire enters the mercurycompartment 59, together with a trace of electrolyte .that may remain.

Thus the transfer of any substantial amount of electrolyte to themercury'compartment is prevented. Notwithstanding this, it is found thatif the wash water is supplied directly to the washing compartment, themercury will become dirty after a time and lose a part of its surfacetension. Whether this is due to exposure to the air or to a slightcontamination with electrolyte or to some other cause is not certain,but it is known that all trouble from this source is eliminated byintroducing the wash water into the mercury compartment, whence itoverflows into the washingcompartment. This arrangement keeps themercury clean and bright.

It will not be necessary to go into the details of the electro-chemicalaction which takes place, it being known that with an electrolyte of thetype disclosed herein the flow of the electric current will cause theremoval of metal from certain metallic anodes, the metal removed formingsoluble salts. Generally speaking, this is what takes place in theapparatus described, when tapering wire made from the alloypreviouslyreferred to herein. It may be mentioned that the iron in the alloy tendsto plate out on the cathode to some extent. This does no harm. Anobjectionable feature, however, is that the silicon forms an insolublecompound, a form of water glass, which after a time tends to clog thepassages for the flow of electrolyte through the cells. This objectionis not serious and can be overcome by the installation of a filter,preferably in the pipe connection which returns the electrolyte from thecollecting trough to the main tank.

When the current is first turned on, it is substantially equally dividedbetween the individual electrolytic cells. This is to be expectedbecause the current divides in accordance with the resistance of thecells and the cells are all alike and have approximately the sameresistance. 7

A substantial part of the total resistance of each cell, however, is theresistance of the wire itself. The result is that as the operationproceeds and the wire in the apparatus becomes tapered, the resistancesof the several cells do not remain the same, but begin to increase inaccordance with the increasing wire resistance at such cells. The wirein the apparatus becomes tapered from left to right, that is, theentering wire at the left always has the same original diameter, whilethe emerging wire at the right becomes progressively smaller, andaccordingly the increase in cell resistance is progressive from left toright, being a maximum in the last cell.

Now the total current through all the cells is maintained constant, andsince it must divide between the several cells in accordance with theirrespective resistances, a gradual current shift takes place as thetapering operation proceeds, the current progressively decreasing in thecells toward the right and progressively increasing in the cells towardthe left of the center of the apparatus. The current shift correspondsto the taper on the wire in the apparatus at any instant but is notproportionate in extent or amount because the wire resistance at anycell constitutes only a part of its total resistance, the remainingresistance being independent of the size of the wire. It follows thatthe amount of current shift is considerably less than would be expectedfrom a consideration of the difference between the size of the wire atthe entering end and its size at the emerging end of the apparatus. Forexample, in the manufacture of the tapered wire previously referred toherein, which tapers from a larger diameter of 4.9 mils to a smallerdiameter of 1.4 mils, the current in the last cell drops from an initialvalue of about .8 ampere to a final value of about .28 ampere. The finalvalue is therefore about one third the initial value. At the first cellthe current rises from an initial value of about .8 ampere to a finalvalue of about 1.3 amperes.

The shift in the current toward the entering end of the apparatusaffects the current density somewhat. At the start of a taperingoperation the current density is approximately the same at all thecells. At the end of the operation there is an overall increase in thecurrent density, due to the current being maintained constant and to.the reduction of the area of wire in the apparatus which is exposed. tothe electrolyte. This increase is distributed between the several cellsin accordance with the current they carry and the area of the wire inthe electrolyte, and is a maximum at the first cell. At the last cellthe increase is very small and the current density may be considered asremaining substantially constant, the decrease in the size of the wirejust about compensating for the decrease in the current. If the wire isbeing reduced to a smaller diameter than 1.4 mils the current density inthe last cell may decrease slightly toward the end of the operation butnot enough to interfere with the production of a satisfactory smoothfinish on the wire.

30 The shift in the current toward the entering end of the apparatusalso affects the amount of work done at the several cells in removingmetal from the wire, the amount of metal removed being proportional tothe current. .At thestart the several cells do equal amounts of work,but

as the taperingof a wire proceeds, a shift in. the work takes placewhich corresponds to the current shift. This work shift modifies theoperation somewhat, but it does not appear to greatly affect thecalculations of wire speeds based on the amount of metal to be removedat the several sections. It has been observed that there is no verysharp demarcation between the end of the tapered section and thefollowing cylindrical section, the corner being slightly rounded off, soto speak. This effect has been attributed to the work shift. It isgenerally advantageous rather than otherwise, but can be corrected ifdesired by a change in the wire speed.

It will .be understood that in setting the'apparatus up for themanufacture of any particular tapered wire, the first few lots of wiremade should be carefully tested to ascertain how closely they conform tothe requirements, and appropriate adjustment of the wire speeds shouldbe made iffound to be necessary. No adjustment may be required, but ifit is, the results'of the tests will indicate where the adjustmentshould be made and the degree of change that is necessary. Having oncedetermined the correct wire speeds, it will be found that substantiallyuniform resistance'wires having required characteristics may be turnedout by careful adherence to such speeds and by maintaining constant theother factors which affect the operation.

The apparatus described herein may also be used to manufacture'very finewire'which cannot be made by the usual drawing operations.

'In this connection it may be explained that the smallest wire which itis practicable to make by drawing is about 2 mils in diameter. Smallerwire can be made but only at agreat expense. By means of the presentinvention wire having a diameter of about 2 mils or more, such as can bereadily made by drawing, can readily be reduced to any desired smallerdiameter down to 1 mil or less by pulling it through the apparatus at aconstant speed. The first few feet of wire, depending on the length ofthe apparatus, will of course be tapered but the remainder will be ofuniform cross-section. The Wire speed will de pend on the amount ofreduction which is to take place, and can be calculated or determinedexperimentally.

In the foregoing a considerable amount of specific information has beengiven as to the construction of the apparatus and the method ofoperating the same; but it will be understood that this has been done tofacilitate the explanation of the principles involved and to affordinformation as to one way in which they may be employed in thesuccessful practice of the invention. Without departure from theseprinciples, numerous variations and modifications may be made, both asto the apparatus and. the method of procedure and. we do not, therefore,wish to be limited to the exact disclosure herein, but desire to includeand have protected all forms and modifications of the invention whichcome within the scope of the appended claims.

We claim:

1. The method of making a tapered wire by means of a plurality ofelectrolytic cells arranged in a row, said wire including two sectionseach

1. THE METHOD OF MAKING A TAPERED WIRE BY MEANS OF A PLURALITY OF ELECTROLYTIC CELLS ARRANGED IN A ROW, SAID WIRE INCLUDING TWO SECTIONS EACH EQUAL IN LENGTH TO THE LENGTH OF SAID ROW, WHICH CONSISTS IN INSERTING THE FIRST OF SAID SECTIONS IN SAID CELLS, PASSING CURRENT THROUGH SAID CELLS WITH SAID WIRE FUNCTIONING AS THE ANODE, PULLING SAID FIRST SECTION AXIALLY OUT OF SAID CELLS AND THE SECOND SECTION AXIALLY INTO SAID CELLS AT CONSTANT SPEED, THEREBY TAPERING SAID FIRST SECTION, AND PULLING SAID SECOND SECTION AXIALLY OUT OF SAID CELLS AT A PREDETERMINED SLOWER CONSTANT SPEED SUCH THAT A TAPER IS PRODUCED ON THE SECOND SECTION HAVING THE SAME SLOPE AS THE TAPER PRODUCED ON THE FIRST SECTION.
 2. APPARATUS FOR THE TAPERING OF A MOVING CONDUCTOR BY ANODIC REDUCTION, SAID APPARATUS COMPRISING, IN THE DIRECTION OF CONDUCTOR MOVEMENT, A COMPARTMENT CONTAINING AN ELECTROLYTE, A COMPARTMENT CONTAINING WASH WATER, AND A COMPARTMENT CONTAINING MERCURY, SAID COMPARTMENTS HAVING SLOTTED WALLS TO PERMIT SAID CONDUCTOR TO BE PULLED THROUGH ON A STRAIGHT LINE, TWO COMPARTMENTS LOCATED BELOW SAID STRAIGHT LINE AND BETWEEN SAID ELECTROLYTE COMPARTMENT AND SAID WASH WATER COMPARTMENT FOR RECEIVING ELECTROLYTE AND WATER, RESPECTIVELY, WHICH LEAKS THROUGH THE SLOTS IN THE WALLS OF THE ELECTROLYTE AND WASH WATER COMPARTMENTS, A CATHODE IMMERSED IN SAID ELECTROLYTE, AND A METALLIC MEMBER IN SAID MERCURY COMPARTMENT ELECTRICALLY CONNECTED TO SAD CONDUCTOR BY THE MERCURY THEREIN. 